Did big life start on land or under water? That's a new question to me... Some evidence shows life was terrestrial 650,000,000 years ago, as presented in Gregory Retallack's paper in Nature. I've seen some of these kinds of layers at Wilpena Pound in South Australia, and they looked like ancient low water sediments to me. In fact what looked like a long worm Dickinsonia stared at me from under a smooth layer in a bluff there – but these layers could have dried from time to time past. Might plants have pronged up then, some with hold fasts?